An active matrix/organic light-emitting diode (AMOLED) display is one of the current hotspots in the research field of flat-panel displays. An organic light-emitting diode (OLED) has such advantages as low power consumption, low production cost, self-luminescence, wide viewing angle and rapid response. As a core technology of the AMOLED display, the design of a pixel driving circuit is significant and important.
For the AMOLED display, a stable current is required so as to control the OLED to emit light. Due to the limitations of the manufacture process and the aging of elements, a threshold voltage (Vth) of a driving transistor for each pixel in the AMOELD display will be drifted, which thus results in a change of the current flowing through the OLED of each pixel along with the threshold voltage. As a result, the display brightness is uneven, and thereby an image display effect will be adversely affected.
As shown in FIG. 1, an existing, basic AMOLED pixel driving circuit merely includes one driving transistor DTFT, one switching transistor T1 and one storage capacitor Cs. When the pixels in one row are to be scanned by a scanning line, a scanning voltage Vscan on the scanning line is a low level, T1 is turned on and a data voltage Vdata is written into the storage capacitor Cs. After the scanning of this row is completed, Vscan changes to be a high level, T1 is turned off, and DTFT is driven by a gate voltage stored in Cs to enable DTFT to generate a current for driving the OLED, thereby to ensure the OLED to emit light continuously within one frame. The current IOLED flowing through the OLED is equal to K(VGS−Vth)2, where K is a constant, VGS is a gate-source voltage of DTFT, and Vth is the threshold voltage of DTFT. Just as mentioned hereinbefore, due to the limitations of the manufacture process and the aging of elements, the threshold voltage Vth of the driving transistor DTFT for each pixel will be drifted, which thus results in a change of the current flowing through the OLED of each pixel along with the threshold voltage Vth. As a result, the image display effect will be adversely affected.
An existing pixel driving circuit having a threshold compensation function may be a 6T1C-based pixel driving circuit, where excessive thin film transistors (TFTs) and lines are used. Though it is able to meet the requirement of threshold compensation, an aperture ratio of the pixel will be reduced correspondingly. In addition, the existing pixel driving circuit is arranged within each pixel unit, so the OLEDs are distributed in a too compact manner.